There is nothing more frustrating than trying to insert a stubborn, poorly made coupler. Having the line charged with air only makes matters worse! These have a unique spring action sleeve for quick connections of air hoses and air tools. Simply pull back on the outer ring (it'll click open into the receiving position), then insert your coupler. You're done! Say goodbye to struggling with ill fitting couplers. Compare this coupler against others and you'll notice ours has a larger diameter air passage that provides more air flow through the coupler to improve the performance of all of your air powered tools and HVLP spray guns. Set includes 1 coupler and 3 male inserts with standard 1/4" NPT fittings. Made in Denmark.